1. Field Of The Invention
The invention relates to improved carbon and graphite articles and a method for making them. Principally, it concerns a noncarcinogenic agent for use in the impregnation step of the carbon or graphite production process, and articles resulting from the use thereof.
2. Description Of The Prior Art
In the manufacture of carbon and graphite electrodes and other carbon and graphite bodies, carbon filler material is mixed with a carbonaceous binder, such as coal tar pitch, and the mixture is formed into desired shapes, for example by extrusion or molding. The bodies thus obtained are baked to high temperatures, typically up to about 900.degree. C., to carbonize the binder and set the mass. The baked bodies may then be heated at temperatures above 2000.degree. C. to effect graphitization.
If desired, the baked bodies may be densified prior to graphitization by impregnation, conventionally with petroleum pitch or the like, the impregnation step comprising preheating the bodies, typically at temperatures in the range of about 275.degree.-300.degree. C., and then impregnating the heated bodies at temperatures of about 225.degree.-250.degree. C. The impregnated bodies may be rebaked prior to graphitization to carbonize the impregnant. Optionally, the impregnation and rebaking steps may be repeated.
For some purposes, the baked articles may be graphitized prior to impregnation, optionally followed by rebaking and regraphitizing.
Until the present invention, only impregnants of petroleum or coal origin were known in the carbon and graphite article production art. A disadvantage of using these impregnants is that they contain polynuclear aromatic hydrocarbons which are known carcinogens in humans (Sax, Dangerous Properties Of Industrial Materials, Fourth Edition, 1975, pp. 279, 564 and 1006). Therefore, avoidance of the use of these types of impregnants in the carbon or graphite industry would tend to decrease the danger of the working environment in and around the impregnation facility of the production plant. Additionally, the high temperatures required for the conventional impregnation process, including preheating, are undesirable.